Many different types of clamps have been tried for the purpose mentioned with varying degrees of success. A common type which is used in low and medium pressure applications generally consists of a single length of band material to surround the article to be clamped, equipped with radially outwardly extending ears and a bolt and nut connection between the ears to pull them together. A tongue attached to one end underlies the other end to close the gap between them. This type is not satisfactory for high pressure applications because the bolt load will pull the ears together and bend them out of shape before the desired tension is achieved in the band. Moreover, the outwardly extending ears are inconvenient and hazardous under many conditions of use.
To overcome these disadvantages another type of clamp was developed using a buckle having top, bottom, and side walls providing a generally rectangular longitudinal passage therethrough. A band was provided having a first end portion anchored to the buckle, an intermediate portion wrapped on itself in spiral fashion with two or more layers extending through the passage to form a generally circular structure surrounding the body to be clamped, and a second end portion extending generally tangentially from the buckle. A tightening tool was then set to thrust against the buckle and grip the second end portion, pulling it through the buckle until the desired tension was produced. The tool was then swung in a direction to bend the end portion upward in front of the near edge of the buckle while maintaining the tension in the band, after which the excess material was sheared or broken off. The upturned remainder was thus anchored against the buckle to maintain the tension and there was no structure extending outward of the buckle to interfere with handling operations. However, since the anchorage was only the bent end of the band it frequently flattened out under the high tension and the band slipped through the buckle, losing all its gripping power.
An effort to improve the clamp just described is disclosed in U.S. Pat. No. 3,833,969 to Hollingsworth. In this patent Hollingsworth uses a very similar basic structure but changes the type of locking means. He forms registering apertures in the top and bottom walls of the buckle and also an aperture in the intermediate portion of the band near its anchorage to the buckle and also in registry with the aperture in the bottom wall of the buckle. After the band is pulled to the desired tension in the same manner as described above he places the point of a center punch in the aperture in the top wall and strikes the punch one or more times with a mallet. The force of the blows deforms the intermediate layers of the band into a plurality of inwardly extending dimples nesting with each other and extending partly into the aligned apertures in the first layer of the band and the bottom wall of the buckle. Their interference with the apertures and with each other serve as a lock against slippage and represent a considerable improvement over the type previously described. However the cam surface effect still allows initial slippage in use at levels lower than desired, particularly because the dimple of the outermost layer tends to flatten and slide out of the next dimple.
The U.S. Pat. No. 3,754,303 to Pollock shows a similar construction in which the buckle is made of a much heavier gauge material than the band, and is relatively very rigid. In this patent an integral area in the top wall is made much thinner than the balance of the buckle, partially segregated by narrow slots to allow deformation and partially connected by short webs. When the band is tightened in the same way as previously described a punch is applied to the center of the thinned area and driven inward by mallet blows. The force of the punch forms a dimple in the thinned section and in each of the underlying layers of the band with the lowermost dimple entering into an aperture in the bottom wall of the buckle. The final result is about the same as in Hollingsworth but the location of the dimpled thinned area, which is integral with the buckle, in the nested dimples probably increases the resistance in initial slippage to a substantial degree. Nevertheless, the cam surface relation of all of the elements makes them quite susceptible to slippage under high tension.